Eosinophilic esophagitis (EoE), a rapidly emerging allergic disease affecting all ages, presents with esophageal food impaction, dysphagia, growth problems, and esophageal stricturing. A non-invasive method to assess disease activity in EoE patients is needed. We believe that a urine or serum test to assess disease activity in EoE patients will be useful clinically and will help increase our understanding of this disease. The long-term goal of this research is to improve non-invasive methods to assess disease activity in EoE patients and increase our knowledge of EoE biology. The objective of this proposal is to identify urine and serum metabolites associated with EoE disease activity. The central hypothesis of this research is that the inflammatory process and the large number of eosinophils sloughed into the intestinal tract of EoE patients results in altered urine and/or serum levels of metabolites which could serve as biomarkers. This hypothesis is strongly supported by our own preliminary analyses of samples from our urine repository. The rationale underlying the proposed research is that identification of EoE metabolite biomarkers would allow easy, inexpensive, non- invasive assessment of EoE disease activity, thus obviating the need for repeated endoscopy and allowing easy longitudinal follow-up of EoE patients. We will test our central hypothesis by pursuing the following Specific Aims: 1. Eosinophil metabolome characterization: we will describe the major and minor metabolites in a preparation of purified eosinophils. This will enable us to target these metabolites (with Mass Spectroscopy inclusion lists) in subsequent urine assays, thus increasing the sensitivity of our analysis. 2. Urine candidate biomarker search: find targeted and global urine metabolites associated with active EoE. Our preliminary data establish proof of principle that specific urine metabolite concentrations are markedly increased in EoE patients. In the proposed research we will target the eosinophil metabolites from Specific Aim 1 and also perform a global urine analysis using mass spectrometry. 3. Serum candidate biomarker search: find targeted and global urine metabolites associated with active EoE. We will use the approach described in aim 2 to analyze existing samples from the well-characterized EoE serum collection of Dr. Mirna Chehade. This contribution will be significant because it will replace endoscopic biopsies as a method of monitoring disease activity in patients with established EoE, thus moving this field from use of an expensive endoscopy with significant risks to use of a readily available noninvasive test which will facilitate long term follow-up and enable easy assessment of response to therapy. The proposed research is innovative because it would present an entirely new method of assessing disease activity in patients with diagnosed EoE. This would truly change the landscape of EoE research and clinical care (i.e. a paradigm shift).